1. Field of the Invention
The present invention relates to a waveguide unit for transmitting and processing microwave or millimeter wave signals. In particular, the present invention relates to the waveguide unit including a waveguide type-polarized wave converter which is interposed between a vertically polarized waveguide and a horizontally polarized waveguide for converting their polarization-planes.
2. Description of Related Art
For a transmission path of a micro wave or millimeter wave band, for example, a rectangular waveguide having sides with one-to-two relation has generally been used.
In order to convert vertically polarized wave signals to horizontally polarized wave signals, further, a twisted waveguide 1 as shown in FIG. 11 has been conventionally utilized, the twisted waveguide 1 being made of e.g. aluminum, copper, or copper pyrites. In the drawing, when vertically polarized wave signals enter into a left end opening, their polarization-planes are gradually changed or turned along the axis of the unit and horizontally polarized wave signals are finally output from its right end opening. The above conventional waveguide assures small reflecting performance over the broad band, but, due to the structure in which the waveguide is gradually twisted, it requires for considerable length in the direction to which electromagnetic waves travel, resulting in size or weight increase. The conventional waveguide also requires a high-definition curved surface, therefore, an advanced manufacturing technique is required, causing high manufacturing cost and unsuitability for high volume production.
The unexamined Japanese patent publication No.83/170201 discloses an another example of a conventional waveguide type-polarized wave converter. FIG. 12 shows a perspective view of the converter described in the Japanese patent publication and illustrates a state in which connecting flanges are disassembled for better understanding.
As shown in FIG. 12, a waveguide type-polarized wave converter 4 made of a thin metal plate is connected between a vertically polarized waveguide 2 and a horizontally polarized waveguide 3 via their respective flanges 2a, 3a. The waveguide type-polarized wave converter 4 is provided with a resonant window 5 with slits 6a, 6b at the center. The vertically polarized wave microwave signals that arrived to the resonant window 5 through the vertically polarized waveguide 2 are converted to a horizontally polarized wave component due to asymmetry in the shape of the slits 6 relative to the direction of an electric field. The converted signals are output from the horizontally polarized waveguide 3. The shape of the slit 6 is optimized so that polarized wave signals can produce resonance at the specific frequency and the vertically polarized wave component can be totally converted to the horizontally polarized wave component. This structure ensures size and weight reduction in the unit, but makes narrow the frequency bandwidth which will be able to obtain a proper reflecting characteristic because of the use of localized resonance phenomenon at the slit 5.
Therefore, it is not applicable to communication systems using the broad frequency bandwidth. Furthermore, because the resonance window is formed with the slit provided in the thin metal plate, it is difficult for the converter to be unified with other waveguide parts, resulting in unsuitability for mass production.